This invention relates to an interconnected combustion system and more particularly to a cross-ignition assembly for interconnecting adjacent combustors in a gas turbine.
A combustion system for a gas turbine commonly includes a number of generally cylindrical combustors disposed about the turbine in an annular arrangement, with each combustor supplying a motive fluid to an arcuate section of a turbine nozzle. It is common practice to interconnect the combustion chambers of adjoining combustors by means of short conduits or "cross-fire tubes" as part of a cross-ignition assembly, the purpose of which is to provide for the ignition of fuel in one chamber from ignited fuel in an adjacent chamber in order to obviate the need for providing a spark plug or the like for each combustor. Additionally, the cross-ignition assembly to some extent also effects an equilization of pressures in adjacent combustors.
A conventional cross-ignition assembly includes cross-fire tubes extending between adjacent combustors. The cross-fire tubes are generally held in place by mounting means which position the opposite ends of the cross-fire tubes in fluid passages formed in the combustion chambers. However, in some such conventional arrangements, the mounting means can inaccurately position the tube ends with respect to the combustion chambers, extending them too far into the combustion gas flow paths therein. This results in damage of cross-fire tubes in the form of end burning. Additionally, cross-fire tubes are often loosely retained in their respective mounting means and are subject to vibration and rotation therein. Typically these mounting means are also loosely affixed to their respective combustor housings or combustion chamber liners, and they are induced to vibrate therein by the oscillation of the retained cross-fire tubes. Such vibration of cross-fire tubes and the mounting means has been found to cause wear and distortion in the cooperating combustor housings and chamber liners, requiring their repair or replacement.
The maximum operating temperature of a cross-fire tube is typically located at its midsection. This is also the most highly stressed structural section of a tube in a conventional cross-ignition assembly wherein the tube is supported at both ends. This combination of temperature and stress makes the cross-fire tube prone to collapse at its midsection. Upon collapse of a cross-fire tube, the combustion gases normally channeled thereby between adjacent combustors may be released to impinge upon the combustor housings. In the past this has lead to overheating and rupture of combustor housings. In an attempt to lower the operating temperature at the midsection of the cross-fire tube, cooling holes or apertures have been provided around the midsection to enable cooling air to enter the tube at that section; however, the cooling obtained by this approach is non-uniform. Additionally, attempts have been made to locate the critical structural sections of cross-fire tubes away from their midsections. This typically has involved use of a cantilever support design wherein the tube members are welded to combustor housings. Such an assembly is disclosed in U.S. Pat. No. 3,001,366 issued Sept. 26, 1961, to L. W. Shutts. However, the welding of a cross-fire tube to a combustor housing gives rise to costly weld repairs, made necessary by thermal cracking or handling damage at the welds, which complicates cross-fire tube replacement.
Furthermore, combustor maintenance in a conventional interconnected combustion system requires that the cross-fire tube ends cooperating with the combustor of interest be withdrawn therefrom. In those systems employing single piece cross-fire tubes, the withdrawl of the tubes from one combustor necessitates their further insertion into the adjacent interconnected combustors. This in turn requires the disassembly of the mounting means in the interconnected combustors in order to obtain access to the combustor of interest, which procedure greatly complicates maintenance efforts.
Accordingly, an object of the present invention is to provide a new and improved cross-ignition assembly for interconnecting adjacent combustors in a gas turbine.
Another object of the present invention is to provide a new and improved cross-ignition assembly including a cross-fire tube especially adapted for facilitating combustion system maintenance.
Another object of the present invention is to provide a new and improved cross-ignition assembly for reducing cross-fire tube end burning and vibration induced wear problems.
Still another object of the present invention is to provide a cross-ignition assembly including improved means for supporting the ends of the cross-fire tube and for cooling the midsection thereof in a manner effective for preventing tube collapse and the attendant damage to combustor housings.